Conventional computer networks are bi-directional, allowing data communication in both directions between servers and clients. Transmitting data over these bi-directional data networks has been a mainstay of computer technology for many years and the communication protocols are well established. Under conventional communication protocols, it is common for the client to initiate connection with the server and to request desired data from the server. As part of the request, the client sends information pertaining to how the data should be sent. For example, the client might include a client address, TCP port number, and so forth.
Digital data, whether transmitted over a wire-based distribution network (e.g., local area network, wide area network, cable, etc.) or a wireless distribution network (e.g., satellite, RF, paging, etc.), is typically packetized and sent over the network in individual packets. Some protocols call for fixed size packets, while other protocols utilize variable size packets. To improve transmission efficiency and to keep pace with the exploding demand for digital information, there is a constant design objective to pump increasingly more data through the same bandwidth pipeline over the network.
One way to achieve this objective is through packet compression. Packets are compressed at the server, transmitted in their compressed state over the network, and decompressed at the client. Apart from compressing whole packets, another solution is partial packet compression in which portions of the packet, such as a header or a data payload, are compressed. One technique for compressing packet headers is discussed in an article by V. Jacobson, entitled "Compressing TCP/IP Headers for Low-Speed Serial Links," and found at the web site http://ds.internic.net/rfc/rfc1144.txt. The Jacobson technique provides an elaborate and complex compression scheme that reduces a 40-byte TCP/IP (Transmission Control Protocol/Internet Protocol) packet header to a three-byte compressed header. The compressed header has an encoded change to the packet ID, a TCP checksum, a connection number, and a change mask. The hardware and/or software used to implement the Jacobson technique must perform sophisticated computations that compress the 40-byte header to the three-byte compressed header, and then subsequently decompress the compressed header to reproduce the uncompressed header.
Apart from the classic bi-directional data networks, there is an increasing interest in the use of broadcast or multicast networks to deliver computer data and other content to clients. These types of distribution networks are unidirectional. Data flows from the server to the clients, but no return communication is possible over the same communication path. As a result, a unidirectional broadcast network cannot support the common protocols used for two-way communication over a bi-directional network, such as client-driven connections and data requests, because the clients are unable to communicate over the broadcast communication link to the server.
Like the bi-directional networks, there is benefit in sending compressed data packets over unidirectional broadcast networks. This invention is directed to a packet header compression technique that improves upon the Jacobson compression scheme, and that is specifically tailored for unidirectional broadcasts.